Three coordination architectures, namely, {Ca2(H2O)4[(NO3)⊂Q*[5]]}2(NO3)6·26H2O (1), {Sr2(H2O)3(NO3)[(NO3)⊂Q*[5]]}(NO3)2·7H2O (2), {Ba(H2O)[(H2O)2 ⊂ Q*[5]]}–(NO3)2·11H2O (3), have been synthesized by reactions of the corresponding alkaline-earth metal salts with pentacyclopentanocucurbit[5]uril (Q*[5]). These compounds were characterized by single-crystal X-ray diffraction studies, showing that the ionic radius of the alkaline-earth metal plays a crucial role in determining which type of molecular capsule forms. Compound 1 is an incompletely closed molecular capsule, compound 2 corresponds to a closed molecular capsule, and compound 3 resembles an opened molecular capsule. The thermogravimetric analysis (TGA) of compound 2 was also characterized.
![Graphical abstract: Ionic radius-dependent self-assembly of closed/opened molecular capsules based on pentacyclopentanocucurbit[5]uril](http://hg.y866.cn/compound/lib/scimg/usr/1/C2RA20569F.jpg)
